Lithography methods are widely used in the production of microscopic structures in a variety of electronic devices such as semiconductor devices and liquid crystal devices. Ongoing miniaturization of the structures of these devices has lead to demands for further miniaturization of resist patterns used in these lithography processes.
Currently, in the most up-to-date fields, fine resist patterns with a line width of approximately 90 nm are able to be formed by lithography. In the future, however, even finer pattern formation will be required.
In order to enable the formation of these types of ultra fine patterns of less than 90 nm, the development of appropriate exposure apparatus and corresponding resist is the first requirement. With respect to the exposure apparatus, techniques such as shortening the wavelength of a light source for F2 excimer lasers, extreme ultraviolet radiation (EUV), electron beams, X-rays, and soft X-rays or increasing the number of aperture (NA) of a lens are being developed.
However, shortening the wavelength of the light source requires a new and expensive exposure apparatus. Furthermore, if the NA value is increased, since the resolution and the depth of focus exist in a trade-off type relationship, even if the resolution is increased, a problem arises in that the depth of focus is lowered.
Recently, as a lithography technology for allowing such problems to be solved, a method known as immersion exposure has been reported. In this method, exposure is conducted in a state where liquid refractive index media such as pure water or a fluorine-based inert liquid (e.g., refractive index liquid and immersion liquid) is disposed in a predetermined thickness on at least a resist film between a lens and the resist film formed on a substrate. In this method, the space of an exposure light path conventionally filled with inert gas such as air or nitrogen is replaced with a liquid having a larger refractive index (n), for example pure water to attain high resolution without a decrease in focal depth width in a manner similar to the use of a light source of shorter wavelength or a high NA lens even if the optical source having the same exposure wavelength is employed.
Such liquid immersion lithography has been remarkably noticed because the use thereof allows a lens implemented in the existing device to realize the formation of a resist pattern excellent in higher resolution property as well as excellent in focal depth in low costs.